The present invention is directed to a highly efficient water distillation process and an apparatus thereof and more particularly, the present invention is directed to a highly efficient water distillation process which minimizes fouling and scaling of operating equipment over long periods of operation.
Generally speaking, water distillation is a highly effective method of vaporizing a pure water distillate and recovering a concentrated liquid containing a large quantity of non-volatile components. This process method can be an effective means to recover clean pure water from contaminated sources. However, water distillation processes typically have several problems not the least of which can be fouling or scaling of the apparatus With minerals or other components from the fluid being distilled. Common scaling compounds consist of calcium, magnesium and silicon. Fouling, or to a greater extent, scaling of the heat transfer surfaces have a detrimental effect on the capacity of the heat transfer components, causing conventional distillation processes to become inoperable.
Another common problem with typical water distillation processes is that of the high energy input requirements. Without a means to effectively recover the input energy, the energy required is equivalent to the latent heat of vaporization of water at a given pressure/temperature. Water distillation, under this condition is not commercially viable for water remediation applications.
Several variables must be considered to overcome the problems with conventional distillation methods. The following three equations describe the basic heat transfer relationships within a water distillation system:                               Q                      (            total            )                          =                  U          *          A          *          LMTD                                    (        1        )                                          Q                      (                          sensible              ⁢                              xe2x80x83                            ⁢              heat                        )                          =                  m          *          CP          *                      (                          T1              -              T2                        )                                              (        2        )                                          Q                      (                          latent              ⁢                              xe2x80x83                            ⁢              heat                        )                          =                  m          *          L                                    (        3        )            
In order to have an efficient distillation system, the quantity of heat exchanged and recovered, Q, expressed by the above stated equations, must be maximized, while at the same time obeying the practical limits for the remaining variables and preventing scaling and fouling. For a given fluid and fluid dynamics within a given heat exchange apparatus, the variables, U, Cp and L are relatively non-variable. Therefore, careful consideration must be given to the variables A, Q/A, LMTD, m, and T1 and T2 to overcome the problems associated with distillation of contaminated water.
To fully overcome the problems related to distilling contaminated water and eliminate scaling, other essential factors must be considered beyond the basic equations stated above:
the rate by which the heat is transferred within the distillation system, known as heat flux or QAxe2x88x921 (Btu hrxe2x88x921 ftxe2x88x922)
the level of contaminates in the concentrate;
the final boiling point of the concentrate relative to the saturation temperature of the vapor stream;
the degree of supersaturation and level of precipitation of the concentrate; and
level of vaporization of the evaporating stream.
Until the advent of the present invention, maximizing the quantity of heat transferred and recovered with a water distillation process, without the tendency of fouling or scaling, could not be realized over a long term continuous period.
A process has been developed which is both energy efficient and eliminates the problems of scaling previously encountered in the distillation of contaminated water, contaminated with organics, inorganics, metals, inter alia.
The invention further advances the concepts established in the initial application. These former concepts linked two distinct concepts, both of which have been previously identified singularly in the prior art, but which have not been uniquely configured with the synergistic effect that results with the present invention. It has been found by combining a conventional vapor recompression circuit and excess low grade heat energy source together with a uniquely configured forced convection heat recovery and transfer circuit, that very desirable results can be obtained in terms of maximizing heat transfer, minimizing compression power requirements and maintaining the desired forced convection circuit non-conductive to scaling exchangers, which is typically encountered by practicing standard distillation methods.
It has now been found that the use of the waste stream energy can be recovered in the heat transfer circuit and this source of low grade energy, most commonly discharged as unrecoverable energy, is employed to reduce the quantity of requisite compression to treat waste water.
By this methodology, the excess vapors passing from the evaporator that are created by the recovered heat energy, do not pass into contact with the compressor, but rather are externally condensed. The result of this is the accumulation of energy, which acts as a driving force for a subsequent crystallization step, leading to the precipitation of solids for disposal.
One object of the present invention is to provide an improved efficient process for distilling water containing organic, inorganic, metals or other contaminant compounds with the result being a purified water fraction devoid of the contaminants which additionally does not involve any scaling of the distillation apparatus.
A further object of one embodiment of the present invention is to provide a method of removing contaminants from a water feed stream containing contaminants, comprising the steps of:
a) providing a water feed stream;
b) providing a source of waste energy for vaporizing the water stream;
c) providing a fluid circulation circuit including a heated separator and a reboiler exchanger in fluid communication;
d) passing the water feed stream into the heated separator;
e) passing the waste energy into the reboiler for recovery of heat energy;
f) vaporizing the water stream with the waste energy in the reboiler exchanger to generate a vapor fraction and a concentrate liquid contaminant fraction;
g) circulating at least a portion of the concentrate liquid fraction through the reboiler exchanger and the heated separator to maintain a ratio of mass of concentrate to vapor fraction of 300 to near 2 to result in a vapor fraction of near 1% by mass to less than 50% by mass exiting the reboiler exchanger to prevent fouling and scaling in the reboiler; and
h) condensing the vapor fraction with an external condensing means;
i) collecting condensed vapor fraction substantially devoid of contaminants.
It has been found that by precisely controlling the ratio of circulating mass in a range of less than 300 to near two times that of the vapor fraction being compressed, several desirable advantages can be realized:
1. The circulating concentrate through the evaporating side of the reboiler will contain a precisely controlled vapor fraction near 1% to 50% of the mass of the circulating concentrate;
2. By precisely controlling this vapor fraction, the temperature rise of the circulating concentrate remains very low (about 1F) and reboiler heat exchange surfaces remain wetted, at a temperature near that of the circulating concentrated fluid. This reduces the risk of fouling of these surfaces;
3. With this controlled low vapor fraction, the concentrated fluid within the exchanger is subjected to a greatly reduced localized concentration factor of less than 1.1, avoiding localized precipitation of scaling compounds on the exchanger surfaces;
4. As the vapor mass is formed toward the exit of the reboiler, the stream velocities within the exchange passages increase significantly promoting good mixing and thus reducing the risk of fouling;
5. By allowing a controlled vapor fraction in the evaporating fluid, significant heat transfer can be realized through the means of latent heat, without scaling and causing a temperature cross within the heat exchanger;
6. Because the temperature rise of the evaporating side of the reboiler is kept very low, the LMTD of the reboiler is maintained, thereby keeping the input energy requirement very low;
7. By adjusting the heat flux, the temperature of the wet surfaces for condensing and evaporating are maintained near that of the saturated steam condition at the evaporating and condensing conditions. The type of boiling experienced will range from primarily forced convection to stable nucleate boiling off the wetted surfaces; and
8. By allowing the reboiling means to absorb low grade waste heat energy, the input power required for compression is reduced and, in some applications, eliminated.
A further object of one embodiment of the present invention is to provide a method of removing contaminants from a water feed stream containing contaminants, comprising the steps of:
a) providing a water feed stream;
b) providing a source of waste energy for vaporizing at least a portion of the water stream;
c) providing a fluid circuit including a heated separator and a reboiler exchanger in communication;
d) providing a vapor circuit including the heated separator, compressor means and the reboiler exchange in communication;
e) passing the water feed stream into the heated separator;
f) vaporizing the water stream with the waste energy and compressed vapor stream in the reboiler exchanger to generate a vapor fraction and concentrate liquid fraction;
g) treating the portion of the vapor fraction created by the waste energy to an external condenser means;
h) recovering remaining portion of vapor fraction by the compressor means;
i) circulating at least a portion of the concentrate liquid fraction through the reboiler exchanger and the heated separator to maintain a ratio of mass of concentrate to vapor fraction of 300 to near 2 to result in a vapor fraction of near 1% by mass to less than 50% by mass exiting the reboiler exchanger to prevent fouling and scaling in the reboiler;
j) collecting the condensed vapor fraction substantially devoid of contaminants.
An even still further object of one embodiment of the present invention is to provide a method of removing contaminants from a water feed stream containing contaminants, comprising the steps of:
a) providing a water feed stream;
b) providing a source of waste energy for vaporizing the water stream;
c) providing a fluid circulation circuit including a heated separator and a reboiler exchanger in fluid communication;
d) passing the water feed stream into the heated separator;
e) passing the waste energy into the reboiler;
f) vaporizing the water stream with the waste energy in the reboiler exchanger to generate a first vapor fraction and a concentrate liquid contaminant fraction;
g) circulating at least a portion of the concentrate liquid fraction through the reboiler exchanger and the heated separator to maintain a ratio of mass of concentrate to vapor fraction of 300 to near 2 to result in a vapor fraction of near 1% by mass to less than 50% by mass exiting the reboiler exchanger to prevent fouling and scaling in the reboiler;
i) providing crystallization means and a reboiler exchanger in communication with the vapor fraction;
j) removing a portion of the concentrate liquid for feed to the crystallization means;
k) passing the vapor fraction into the reboiler for providing heat energy for precipitating solids from the concentrate liquid;
l) creating a second vapor fraction from the crystallization means and a substantially solid fraction stream;
m) condensing the second vapor fraction with condenser means; and
n) collecting condensed first vapor fraction and second vapor fraction.
As further advantages to this methodology, the input costs are effectively zero. This is due to the fact that if sufficient low grade waste energy can be made available, there is no requirement for a compressor to treat waste water. Further still, the method protocol facilitates 100% water recovery and results in a zero waste water effluent solution since the contaminants are converted to solid waste.
A further object of the present invention is to provide a method of of removing contaminants from a fluid feed stream containing volatilizable and nonvolatilizable contaminants, comprising the steps of:
a) providing a feed stream;
b) providing a source of waste energy;
c) preheating the feed stream in a first step to at least partially remove some of the volatilizable contaminants from the feed stream and recover energy from a concentrate and distillate;
d) heating the feed stream in a second heating step in a heated separator to generate a first vapor fraction containing at least a portion of the volatilizable contaminants and a concentrate liquid contaminant fraction;
e) passing the first vapor fraction through a distillation column while in contact with distillate reflex to form a second vapor fraction substantially devoid of contaminants;
f) treating the second vapor fraction in an external condenser means;
g) passing the waste energy into the reboiler exchanger;
h) circulating at least a portion of the concentrate liquid fraction through the reboiler exchanger and the heated separator to maintain a ratio of mass of concentrate to vapor fraction of 300 to near 2 to result in a vapor fraction of near 1% by mass to less than 50% by mass exiting the reboiler exchanger;
i) collecting the condensed distillate of the second vapor fraction substantially devoid of the contaminants; and
j) recirculating a portion of the condensed second vapor fraction to the distillation column as distillate reflux.
A still further object of one embodiment of the present invention is to provide a method of removing volatile and nonvolatile contaminants from a water feed stream containing contaminants, comprising the steps of:
a) providing a water feed stream;
b) providing a source of waste energy in the form of steam at a pressure of less than 100 psi for vaporizing the water stream;
c) providing a fluid circulation circuit including a heated separator and a reboiler exchanger in fluid communication;
d) passing the water feed stream into the heated separator for absorbing energy in the steam;
e) passing the waste energy into the reboiler;
f) vaporizing the water stream with the waste energy in the reboiler exchanger to generate a vapor fraction and a concentrate liquid contaminant fraction;
g) treating the waste energy with the reboiler exchanger to generate a condensed distillate from the reboiler exchanger;
h) circulating at least a portion of the concentrate liquid fraction through the reboiler exchanger and the heated separator to maintain a ratio of mass of concentrate to vapor fraction of 300 to near 2 to result in a vapor fraction of near 1% by mass to less than 50% by mass exiting the reboiler exchanger to prevent fouling and scaling in the reboiler;
i) providing a condenser;
j) passing the vapor fraction from the heated separator into the condenser; and
k) collecting condensed vapor fraction substantially devoid of contaminants.
Broadly, in one possible embodiment, distilled water is evaporated and passed through a mesh pad to remove any entrained droplets, whereas a portion is externally condensed and the remaining portion enters the compressor. The compressor elevates the pressure and temperature of the vapor stream above that of the heated separator to allow effective heat transfer across the reboiler heat exchanger. The vapor stream subsequently combines with the waste energy stream and enters the reboiler where it is xe2x80x9cdesuperheatedxe2x80x9d and condensed to distillate. The heat energy is transferred to the circulating concentrate from the heated separator where, by way of controlling the mass of circulating concentrate to vapor stream, to a range of less than 300 to near 2, less than 50% vapor, more precisely less than 10%, vapor is generated in the circulating concentrate stream. This vapor formed in the circulating concentrate stream absorbs the transferred heat by latent heat of vaporization, while at the same time not allowing the temperature rise on the circulating concentrate to increase greater than about 1F. The clean distillate water, collected from the external condenser and the reboiler exchanger at condensing temperature and pressure, passes through the preheater to recover the sensible heat portion of the system to the incoming feed stream. Simultaneously, a portion of the concentrate stream is removed from the heated separator to control the desired concentration of the non-volatile contaminants. This concentrate blowdown stream at the heated separator temperature and pressure, is passed through an additional preheater to impart the remaining sensible heat energy to the feed stream. Additional pre- and post-treatment techniques can be employed as batch or continuous process methods to remove or contain contaminants, prior to, after or during the distillation operation. Methods of pH control can be used to ionize volatile components or alter solubility conditions in the concentrate to further enhance the subject distillation process. A substantially high level of distilled water can be recovered, typically in excess of 90% of the water feed stream. With the further addition of a crystallization means, 100% water recovery can be achieved.
The distillate water recovered can be controlled to purity level and temperature level which allows it to be reused as process water, reused as distilled water or safely released to nature water sheds meeting or exceeding virtually all environmental water quality standards.
In terms of the breadth for this process, the same could be easily employed to decontaminate industrial processed water such as that in the refinery, petrochemical, pulp and paper, food, mining, automotive/other transportation industries, heavy oil plants and the manufacturing industries. In addition, applications are envisioned for landfill leachate water, desalination, ground water remediation, well water cleanup, lagoon remediation, oil field waste water recovery, as well as producing any form of boiler feed water, and concentrating valuable components from dilute streams. This listing is by no means exhaustive, but rather exemplary.